(a) Field of the Invention
The present invention relates to a rubbing device used in the manufacture of an optical compensation film. More particularly, the present invention relates to a rubbing device that allows for the setting of a rubbing angle with respect to a moving direction of a base film as desired, and enables interconnection of films using a continuous roll-to-roll process.
(b) Description of the Related Art
The optical characteristics of a liquid crystal display panel are controlled by the application of a polarization film, a retardation film, and an optical compensation film. The optical compensation film includes a liquid crystal polymer having a predetermined orientation, and acts to adjust a color shift and a contrast ratio of the liquid crystal panel to ensure a wide viewing angle. A conventional λ/4 retardation film that varies a polarization pattern may be used for the optical compensation film.
Such an optical compensation film is manufactured by performing a rubbing treatment on a surface of the base film such that a valley of a predetermined direction is formed on the surface of the base film, after which a liquid crystal material is deposited on the base film to orient liquid crystal molecules between the valleys.
In the conventional rubbing treatment, a rubbing cloth and the base film are each respectively wound around a rubbing roller and a base roller, and in a state where the rubbing cloth is in contact with the base film, the rubbing roller is rotated in a direction opposite the direction of movement of the base film. As a result, rubbing occurs between the rubbing cloth and the base film. The rubbing direction is typically in the direction of movement of the base film.
However, there are instances when it becomes necessary to set a light transmission axis of the optical compensation film at a predetermined angle with a light transmission axis of the polarization film or another optical compensation film. The light transmission axis of the optical compensation film is determined by the rubbing direction, while the light transmission axis of the polarization film is the same as a stretching direction of the polarization film.
Accordingly, with reference to FIG. 1, a polarization film 1 is tensed in a direction A such that the polarization film 1 is manufactured having a light transmission axis in the direction A. Further, a rubbing treatment is performed on a base film 3 in the direction A while it is also moved in the direction A, and a liquid crystal material is deposited on the base film 3 to thereby produce a light compensation film 5. The light compensation film 5 is then cut diagonally at a predetermined angle.
Subsequently, the polarization film 1 and the light compensation film 5 are combined into an integral unit while each has a light transmission axis of a predetermined angle. (Direction B in the drawing indicates the light transmission axis of the light compensation film 5.)
However, in the above method, since the films are individually manufactured in separate lines before being combined into a single unit, manufacture is complicated and overall production costs are increased. Further, there is waste in the above process in that the unused portion of the film that is cut is simply discarded.
Therefore, there is disclosed an off-axis rubbing process, in which the direction of movement and rubbing direction of the base film are different such that a slanted light transmission axis in a desired direction with respect to a lengthwise direction of the base film is obtained. Off-axis rubbing is typically performed by diagonally moving across the base film with a rotating rubbing cloth.
Korean Laid-Open Patent No. 2000-12120 discloses a method related to the off-axis rubbing process. That is, a method is disclosed in which some of the base rollers are set to be off-axis such that some of the base films are positioned diagonally with respect to rotating rubbing cloths. However, this and other conventional processes that use off-center rubbing have many drawbacks.
In particular, the conventional off-center rubbing process cannot exceed a rubbing angle of 60°, and it is not possible to realize a rubbing angle of 90° or greater. Because of this limitation in the applicable rubbing angle, there are also limits in the variety of light transmission axes that can be obtained for the produced optical compensation films.
Further, with the diagonal positioning of some of the base films, it is possible to form an orientation surface on the base films in an unintended direction, or for friction to be generated such that creases are formed in the base films. This negatively affects the quality and evenness of the liquid crystal material coated on the base films.
Finally, it is difficult to realize various rubbing angles and to freely adjust the rubbing angle with the use of conventional off-axis rubbing. This rules out the possibility of performing a roll-to-roll process to combine the films of the optical compensation film, the polarization film, and other optical compensation films. Hence, manufacture remains complicated and production costs remain high.